The use of transponders to electronically tag animals and birds is well known. Examples of such tags devices are given in Patent Nos. Tags—WO 97/46083 and WO 93/22907 and Rumen Pellet PCT/AU95/00218. The devices take the form of rumen pellets which are ingested to remain in the rumen and/or ear tags which are fastened to the ears or bodies of animals or birds. The devices are designed to enable operators to track livestock from pasture to abattoir as the devices remain in or on the carcasses. Tagging of bovine livestock especially cattle has become important in the control of diseases such as bovine spongiform encephalitis (BSE) and foot and mouth disease. This has become especially relevant for all edible meat throughout world markets, and is now essential where detection of European sourced carcasses is crucial.
Currently, the devices are detected by a transmitting/receiving or a transceiver antenna which can be in the form of a hand operated wand or a fixed antenna which is positioned at an appropriate distance from the carcasses moving past the antenna on a suspended conveyor track. In the case of hand held antennas, this is labour intensive, time consuming with expensive attendant costs, due to increasing numbers of mixed carcasses both with and without devices. This process requires an operator to wave the hand held wand to detect the transponder in or on every carcass. There is a need to read animals of all sizes with either a pellet or ear tag. There is a need to read the devices automatically as 3000 a day may be slaughtered, but only 500 may carry tags and it is essential that the 500 be read. In the case of the fixed antenna, this is a more economical solution as it dispenses with the necessity of having an operator to read every carcass whether it has a device or not although there are other problems with this system. Most abattoirs have some machinery with variable speed drives operating at a frequency in the vicinity of 134 kHz or thereabout. This complies with the ISO standard frequency for which livestock operators must comply with worldwide. As a consequence of the 134 kHz approximate operational frequency, the read range of the transponders by free standing fixed antennae due to interference has been effectively reduced to a third for example, from 1.8 meters to 600 mm. This has resulted in the problem that some readings are missed from transponders on carcasses, which pass the fixed antenna outside the effective read range. One solution to this problem of obtaining a positive reading of the transponder is to have the carcass come into contact and actually brush the antenna. However, having the antenna in a fixed position in the path of a carcass causes too much sideways movement as the carcass brushes the antenna resulting in some carcasses actually falling off the conveyer system causing an increase in down time and possible bruising of the carcasses from swinging and hitting surrounding objects.